/***
 *   Copyright (c) 1995-2008 Cycorp Inc.
 * 
 *   Licensed under the Apache License, Version 2.0 (the "License");
 *   you may not use this file except in compliance with the License.
 *   You may obtain a copy of the License at
 *   
 *   http://www.apache.org/licenses/LICENSE-2.0
 * 
 *   Unless required by applicable law or agreed to in writing, software
 *   distributed under the License is distributed on an "AS IS" BASIS,
 *   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *   See the License for the specific language governing permissions and
 *   limitations under the License.
 *
 *  Substantial portions of this code were developed by the Cyc project
 *  and by Cycorp Inc, whose contribution is gratefully acknowledged.
*/

package com.cyc.tool.subl.util;

import java.security.*;
import java.io.IOException;
import java.io.UnsupportedEncodingException;

/**
 *
 * A class that represents an immutable universally unique identifier (UUID).
 * A UUID represents a 128-bit value.
 *
 * <p>There exist different variants of these global identifiers. The methods
 * of this class are for manipulating the Leach-Salz variant, although the
 * constructors allow the creation of any variant of UUID (described below).
 *
 * <p>The layout of a variant 2 (Leach-Salz) UUID is as follows:
 *
 * The most significant long consists of the following unsigned fields:
 * <pre>
 * 0xFFFFFFFF00000000 time_low
 * 0x00000000FFFF0000 time_mid
 * 0x000000000000F000 version
 * 0x0000000000000FFF time_hi
 * </pre>
 * The least significant long consists of the following unsigned fields:
 * <pre>
 * 0xC000000000000000 variant
 * 0x3FFF000000000000 clock_seq
 * 0x0000FFFFFFFFFFFF node
 * </pre>
 *
 * <p>The variant field contains a value which identifies the layout of
 * the <tt>UUID</tt>. The bit layout described above is valid only for
 * a <tt>UUID</tt> with a variant value of 2, which indicates the
 * Leach-Salz variant.
 *
 * <p>The version field holds a value that describes the type of this
 * <tt>UUID</tt>. There are four different basic types of UUIDs: time-based,
 * DCE security, name-based, and randomly generated UUIDs. These types
 * have a version value of 1, 2, 3 and 4, respectively.
 *
 * <p>For more information including algorithms used to create <tt>UUID</tt>s,
 * see the Internet-Draft <a href="http://www.ietf.org/internet-drafts/draft-mealling-uuid-urn-03.txt">UUIDs and GUIDs</a>
 * or the standards body definition at
 * <a href="http://www.iso.ch/cate/d2229.html">ISO/IEC 11578:1996</a>.
 *
 * @version 1.14, 07/12/04
 * @since   1.5
 */
public final class UUID
implements java.io.Serializable, Comparable {
  
  /**
   * Explicit serialVersionUID for interoperability.
   */
  private static final long serialVersionUID = -4856846361193249489L;
  
    /*
     * The most significant 64 bits of this UUID.
     *
     * @serial
     */
  private final long mostSigBits;
  
    /*
     * The least significant 64 bits of this UUID.
     *
     * @serial
     */
  private final long leastSigBits;
  
    /*
     * The version number associated with this UUID. Computed on demand.
     */
  private transient int version = -1;
  
    /*
     * The variant number associated with this UUID. Computed on demand.
     */
  private transient int variant = -1;
  
    /*
     * The timestamp associated with this UUID. Computed on demand.
     */
  private transient volatile long timestamp = -1;
  
    /*
     * The clock sequence associated with this UUID. Computed on demand.
     */
  private transient int sequence = -1;
  
    /*
     * The node number associated with this UUID. Computed on demand.
     */
  private transient long node = -1;
  
    /*
     * The hashcode of this UUID. Computed on demand.
     */
  private transient int hashCode = -1;
  
    /*
     * The random number generator used by this class to create random
     * based UUIDs.
     */
  private static volatile SecureRandom numberGenerator = null;
  
  // Constructors and Factories
  
    /*
     * Private constructor which uses a byte array to construct the new UUID.
     */
  private UUID(byte[] data) {
    long msb = 0;
    long lsb = 0;
    assert data.length == 16;
    for (int i=0; i<8; i++)
      msb = (msb << 8) | (data[i] & 0xff);
    for (int i=8; i<16; i++)
      lsb = (lsb << 8) | (data[i] & 0xff);
    this.mostSigBits = msb;
    this.leastSigBits = lsb;
  }
  
  /**
   * Constructs a new <tt>UUID</tt> using the specified data.
   * <tt>mostSigBits</tt> is used for the most significant 64 bits
   * of the <tt>UUID</tt> and <tt>leastSigBits</tt> becomes the
   * least significant 64 bits of the <tt>UUID</tt>.
   *
   * @param  mostSigBits
   * @param  leastSigBits
   */
  public UUID(long mostSigBits, long leastSigBits) {
    this.mostSigBits = mostSigBits;
    this.leastSigBits = leastSigBits;
  }
  
  /**
   * Static factory to retrieve a type 4 (pseudo randomly generated) UUID.
   *
   * The <code>UUID</code> is generated using a cryptographically strong
   * pseudo random number generator.
   *
   * @return  a randomly generated <tt>UUID</tt>.
   */
  public static UUID randomUUID() {
    SecureRandom ng = numberGenerator;
    if (ng == null) {
      numberGenerator = ng = new SecureRandom();
    }
    
    byte[] randomBytes = new byte[16];
    ng.nextBytes(randomBytes);
    randomBytes[6]  &= 0x0f;  /* clear version        */
    randomBytes[6]  |= 0x40;  /* set to version 4     */
    randomBytes[8]  &= 0x3f;  /* clear variant        */
    randomBytes[8]  |= 0x80;  /* set to IETF variant  */
    UUID result = new UUID(randomBytes);
    return new UUID(randomBytes);
  }
  
  /**
   * Static factory to retrieve a type 3 (name based) <tt>UUID</tt> based on
   * the specified byte array.
   *
   * @param  name a byte array to be used to construct a <tt>UUID</tt>.
   * @return  a <tt>UUID</tt> generated from the specified array.
   */
  public static UUID nameUUIDFromBytes(byte[] name) {
    MessageDigest md;
    try {
      md = MessageDigest.getInstance("MD5");
    } catch (NoSuchAlgorithmException nsae) {
      throw new InternalError("MD5 not supported");
    }
    byte[] md5Bytes = md.digest(name);
    md5Bytes[6]  &= 0x0f;  /* clear version        */
    md5Bytes[6]  |= 0x30;  /* set to version 3     */
    md5Bytes[8]  &= 0x3f;  /* clear variant        */
    md5Bytes[8]  |= 0x80;  /* set to IETF variant  */
    return new UUID(md5Bytes);
  }
  
  /**
   * Creates a <tt>UUID</tt> from the string standard representation as
   * described in the {@link #toString} method.
   *
   * @param  name a string that specifies a <tt>UUID</tt>.
   * @return  a <tt>UUID</tt> with the specified value.
   * @throws IllegalArgumentException if name does not conform to the
   *         string representation as described in {@link #toString}.
   */
  public static final UUID fromString(final String name) {
    String[] components = name.split("-");
    if (components.length != 5) {
      throw new IllegalArgumentException("Invalid UUID string: "+name);
    }
    //for (int i=0; i<5; i++)
    //  components[i] = "0x"+components[i];
    
    long mostSigBits = Long.parseLong(components[0], 16);//Long.decode(components[0]).longValue();
    mostSigBits <<= 16;
    mostSigBits |= Long.parseLong(components[1], 16);//Long.decode(components[1]).longValue();
    mostSigBits <<= 16;
    mostSigBits |= Long.parseLong(components[2], 16);//Long.decode(components[2]).longValue();
    
    long leastSigBits = Long.parseLong(components[3], 16);//Long.decode(components[3]).longValue();
    leastSigBits <<= 48;
    leastSigBits |= Long.parseLong(components[4], 16);//Long.decode(components[4]).longValue();
    
    return new UUID(mostSigBits, leastSigBits);
  }
  
  // Field Accessor Methods
  
  /**
   * Returns the least significant 64 bits of this UUID's 128 bit value.
   *
   * @return the least significant 64 bits of this UUID's 128 bit value.
   */
  public long getLeastSignificantBits() {
    return leastSigBits;
  }
  
  /**
   * Returns the most significant 64 bits of this UUID's 128 bit value.
   *
   * @return the most significant 64 bits of this UUID's 128 bit value.
   */
  public long getMostSignificantBits() {
    return mostSigBits;
  }
  
  /**
   * The version number associated with this <tt>UUID</tt>. The version
   * number describes how this <tt>UUID</tt> was generated.
   *
   * The version number has the following meaning:<p>
   * <ul>
   * <li>1    Time-based UUID
   * <li>2    DCE security UUID
   * <li>3    Name-based UUID
   * <li>4    Randomly generated UUID
   * </ul>
   *
   * @return  the version number of this <tt>UUID</tt>.
   */
  public int version() {
    if (version < 0) {
      // Version is bits masked by 0x000000000000F000 in MS long
      version = (int)((mostSigBits >> 12) & 0x0f);
    }
    return version;
  }
  
  /**
   * The variant number associated with this <tt>UUID</tt>. The variant
   * number describes the layout of the <tt>UUID</tt>.
   *
   * The variant number has the following meaning:<p>
   * <ul>
   * <li>0    Reserved for NCS backward compatibility
   * <li>2    The Leach-Salz variant (used by this class)
   * <li>6    Reserved, Microsoft Corporation backward compatibility
   * <li>7    Reserved for future definition
   * </ul>
   *
   * @return  the variant number of this <tt>UUID</tt>.
   */
  public int variant() {
    if (variant < 0) {
      // This field is composed of a varying number of bits
      if ((leastSigBits >>> 63) == 0) {
        variant = 0;
      } else if ((leastSigBits >>> 62) == 2) {
        variant = 2;
      } else {
        variant = (int)(leastSigBits >>> 61);
      }
    }
    return variant;
  }
  
  /**
   * The timestamp value associated with this UUID.
   *
   * <p>The 60 bit timestamp value is constructed from the time_low,
   * time_mid, and time_hi fields of this <tt>UUID</tt>. The resulting
   * timestamp is measured in 100-nanosecond units since midnight,
   * October 15, 1582 UTC.<p>
   *
   * The timestamp value is only meaningful in a time-based UUID, which
   * has version type 1. If this <tt>UUID</tt> is not a time-based UUID then
   * this method throws UnsupportedOperationException.
   *
   * @throws UnsupportedOperationException if this UUID is not a
   *         version 1 UUID.
   */
  public long timestamp() {
    if (version() != 1) {
      throw new UnsupportedOperationException("Not a time-based UUID");
    }
    long result = timestamp;
    if (result < 0) {
      result = (mostSigBits & 0x0000000000000FFFL) << 48;
      result |= ((mostSigBits >> 16) & 0xFFFFL) << 32;
      result |= mostSigBits >>> 32;
      timestamp = result;
    }
    return result;
  }
  
  /**
   * The clock sequence value associated with this UUID.
   *
   * <p>The 14 bit clock sequence value is constructed from the clock
   * sequence field of this UUID. The clock sequence field is used to
   * guarantee temporal uniqueness in a time-based UUID.<p>
   *
   * The  clockSequence value is only meaningful in a time-based UUID, which
   * has version type 1. If this UUID is not a time-based UUID then
   * this method throws UnsupportedOperationException.
   *
   * @return  the clock sequence of this <tt>UUID</tt>.
   * @throws UnsupportedOperationException if this UUID is not a
   *         version 1 UUID.
   */
  public int clockSequence() {
    if (version() != 1) {
      throw new UnsupportedOperationException("Not a time-based UUID");
    }
    if (sequence < 0) {
      sequence = (int)((leastSigBits & 0x3FFF000000000000L) >>> 48);
    }
    return sequence;
  }
  
  /**
   * The node value associated with this UUID.
   *
   * <p>The 48 bit node value is constructed from the node field of
   * this UUID. This field is intended to hold the IEEE 802 address
   * of the machine that generated this UUID to guarantee spatial
   * uniqueness.<p>
   *
   * The node value is only meaningful in a time-based UUID, which
   * has version type 1. If this UUID is not a time-based UUID then
   * this method throws UnsupportedOperationException.
   *
   * @return  the node value of this <tt>UUID</tt>.
   * @throws UnsupportedOperationException if this UUID is not a
   *         version 1 UUID.
   */
  public long node() {
    if (version() != 1) {
      throw new UnsupportedOperationException("Not a time-based UUID");
    }
    if (node < 0) {
      node = leastSigBits & 0x0000FFFFFFFFFFFFL;
    }
    return node;
  }
  
  // Object Inherited Methods
  
  /**
   * Returns a <code>String</code> object representing this
   * <code>UUID</code>.
   *
   * <p>The UUID string representation is as described by this BNF :
   * <pre>
   *  UUID                   = <time_low> "-" <time_mid> "-"
   *                           <time_high_and_version> "-"
   *                           <variant_and_sequence> "-"
   *                           <node>
   *  time_low               = 4*<hexOctet>
   *  time_mid               = 2*<hexOctet>
   *  time_high_and_version  = 2*<hexOctet>
   *  variant_and_sequence   = 2*<hexOctet>
   *  node                   = 6*<hexOctet>
   *  hexOctet               = <hexDigit><hexDigit>
   *  hexDigit               =
   *        "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
   *        | "a" | "b" | "c" | "d" | "e" | "f"
   *        | "A" | "B" | "C" | "D" | "E" | "F"
   * </pre>
   *
   * @return  a string representation of this <tt>UUID</tt>.
   */
  public String toString() {
    return (digits(mostSigBits >> 32, 8) + "-" +
    digits(mostSigBits >> 16, 4) + "-" +
    digits(mostSigBits, 4) + "-" +
    digits(leastSigBits >> 48, 4) + "-" +
    digits(leastSigBits, 12));
  }
  
  /** Returns val represented by the specified number of hex digits. */
  private static String digits(long val, int digits) {
    long hi = 1L << (digits * 4);
    return Long.toHexString(hi | (val & (hi - 1))).substring(1);
  }
  
  /**
   * Returns a hash code for this <code>UUID</code>.
   *
   * @return  a hash code value for this <tt>UUID</tt>.
   */
  public int hashCode() {
    if (hashCode == -1) {
      hashCode = (int)((mostSigBits >> 32) ^
      mostSigBits ^
      (leastSigBits >> 32) ^
      leastSigBits);
    }
    return hashCode;
  }
  
  /**
   * Compares this object to the specified object.  The result is
   * <tt>true</tt> if and only if the argument is not
   * <tt>null</tt>, is a <tt>UUID</tt> object, has the same variant,
   * and contains the same value, bit for bit, as this <tt>UUID</tt>.
   *
   * @param   obj   the object to compare with.
   * @return  <code>true</code> if the objects are the same;
   *          <code>false</code> otherwise.
   */
  public boolean equals(Object obj) {
    if (!(obj instanceof UUID))
      return false;
    if (((UUID)obj).variant() != this.variant())
      return false;
    UUID id = (UUID)obj;
    return (mostSigBits == id.mostSigBits &&
    leastSigBits == id.leastSigBits);
  }
  
  // Comparison Operations
  
  /**
   * Compares this UUID with the specified UUID.
   *
   * <p>The first of two UUIDs follows the second if the most significant
   * field in which the UUIDs differ is greater for the first UUID.
   *
   * @param  val <tt>UUID</tt> to which this <tt>UUID</tt> is to be compared.
   * @return -1, 0 or 1 as this <tt>UUID</tt> is less than, equal
   *         to, or greater than <tt>val</tt>.
   */
  public int compareTo(Object obj) {
    if ((obj == null) || (!(obj instanceof UUID))) {
      throw new RuntimeException("Can't compare UUIDs to non-UUIDs: " + obj);
    }
    UUID val = (UUID)obj;
    // The ordering is intentionally set up so that the UUIDs
    // can simply be numerically compared as two numbers
    return (this.mostSigBits < val.mostSigBits ? -1 :
      (this.mostSigBits > val.mostSigBits ? 1 :
        (this.leastSigBits < val.leastSigBits ? -1 :
          (this.leastSigBits > val.leastSigBits ? 1 :
            0))));
  }
  
  /**
   * Reconstitute the <tt>UUID</tt> instance from a stream (that is,
   * deserialize it). This is necessary to set the transient fields
   * to their correct uninitialized value so they will be recomputed
   * on demand.
   */
  private void readObject(java.io.ObjectInputStream in)
  throws java.io.IOException, ClassNotFoundException {
    
    in.defaultReadObject();
    
    // Set "cached computation" fields to their initial values
    version = -1;
    variant = -1;
    timestamp = -1;
    sequence = -1;
    node = -1;
    hashCode = -1;
  }
}
